The present invention relates generally to inkjet printing mechanisms, and more particularly to a curved wiper blade system for removing ink residue from an inkjet printhead in an inkjet printing mechanism.
Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as xe2x80x9cspitting.xe2x80x9d The waste ink is collected at a spitting reservoir portion of the service station, known as a xe2x80x9cspittoon.xe2x80x9d After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper, or a more rigid spring-loaded wiper, that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper.
One way to improve nozzle wiping efficiency is through the use of fluid assisted wiping, where the service station stores a supply of a non-volatile ink solvent fluid, such as glycerol or polyethylene glycol (xe2x80x9cPEGxe2x80x9d), with the wiper occasionally picking up some of the cleaning fluid and transferring it to the printhead nozzle plate. One inkjet printer having such a solvent application system is the Hewlett-Packard Company""s model 2000C Professional Series Inkjet Printer. This wiper fluid also acts as a lubricant to minimize nozzle bore deformation that may occur due to the wiping action. Unfortunately, while the earlier wiper designs allowed for an easy pick and dispense of the fluid onto the nozzle plate, they were not well suited for removing the resulting waste ink and fluid mixture from the nozzle plate.
For instance, FIG. 8 shows a side elevational view of such an earlier wiper system during a wiping stroke, with FIG. 9 being side elevational of a later stage of the wiping stroke, while FIG. 10 shows an enlarged view of an intermediate stage of the wiping stroke. In FIG. 8, we see an inkjet cartridge C having a printhead P which is being wiped by a dual bladed wiper system W, which has a first wiper blade B1 and a second wiper blade B2. The wiper system W is constructed as described in U.S. Pat. No. 5,614,930, currently assigned to the present assignee, the Hewlett-Packard Company. Each of the wiper blades B1 and B2 have wiper tips with an arcuate exterior wiping edge and an angular interior wiping edge as described in U.S. Pat. No. 5,614,930.
When wiping in a direction D, the rounded exterior wiping edge of the first wiper blade B1 is used to wick or draw ink from the nozzles through capillary action. This wicked ink is then moved by blade B1 along succeeding nozzles to dissolve ink residue accumulated on the nozzle plate. The angular interior wiping edge of the second wiper blade B2 then scrapes away the extracted ink and dissolved ink residue, along with any other debris from the nozzle plate P. Unfortunately in some cases, after much use, the second wiper blade B2 was not able to efficiently remove the ink residue from the nozzle plate, and instead, merely spread the dirty fluid mixture over the nozzle plate. In extreme cases, the accumulated dirty fluid/ink mixture could migrate to the sides of the nozzle plate, or to the back of the nozzle area where the printhead receives electrical signals from an electrical interconnect I, corroding the electrical traces on the interconnect or causing electrical shorts between the interconnect traces.
FIG. 10 illustrates another problem associated with the earlier wiper blade designs. The action of FIG. 10 occurs between that shown in FIGS. 8 and 9. In FIG. 8 we see the second wiper blade B2 has just come into contact with the interconnect I. In this flat-to-flat contact position, wiper blade B2 has no ability to wipe ink, ink residue, or any combination thereof from the interconnect I. Quite to the contrary, as shown in FIG. 10, any ink solvent and/or ink residue remaining on the interior surface of the wiper blade B2 is actually cleaned from the wiper blade by the corner between the orifice plate P and the interconnect I, leaving an undesirable deposit of solvent and residue are along interconnect I. Eventually, a large amount of fluid may accumulate along the lower portion of the interconnect I, leading to additional electrical trace corrosion and/or electrical ink shorts caused by ink bridging between the electrical traces.